1. Field of the Invention
The present invention relates to solid milk for drinking upon dissolution in warm water and to a method for manufacturing such solid milk. More particularly, the present invention relates to solid milk with suitable solubility and strength, and to a method for manufacturing thereof.
2. Description of the Related Art
Powdered milk is a food product whose storage ability is improved by completely removing water, which is necessary for the growth of microorganisms, from milk. Because volume and weight are reduced when water is removed, the powdered milk is easy to transport. The powdered milk thus has many advantages in terms of storage ability and transportation. Because pores (spaces) are present between the particles in powdered milk, the porosity of powdered milk is generally 60% to 70% and the milk is easily dissolved in warm water. However, when the powdered milk is dissolved in warm water or the like, the appropriate quantity thereof has to be weighed. Furthermore, the powdered milk is sometimes scattered when it is weighed or removed. Accordingly, solid milk obtained by converting the powdered milk into a solid form was suggested (see Japanese Utility Model Laid-open Publication Nos. S49-130189 and S61-118280). However, it is not easy to convert the powdered milk into a solid state and to satisfy the requirements placed on both the strength and the solubility. In other words, even if the powdered milk is converted into a solid state, it is easily fractured and difficult to handle. Furthermore, the solid milk has a surface area less than that of the powdered milk and is, therefore, difficult to dissolve in warm water.
When powdered milk is actually converted into a solid state by applying a pressure, because the powdered milk is an emulsion, the emulsification state is destroyed by the pressure. As a result, a fat oozes from the powdered milk (this fat is called “free fat”). This free fat is easily oxidized and spoils the taste of powdered milk. Furthermore, the problem associated with dissolving the powdered milk in warm water is that the excess free fat floats and agglutinates (this effect is called “oil-off”). On the other hand, Japanese Examined Patent Publication No. S49-4948 discloses, “aggregated powdered milk”. Furthermore, it discloses “the aggregated powdered milk has a porous internal structure and, therefore, easily absorbs water. As a result, when placed in warm water, it is easily disintegrated, dispersed, and dissolved”. However, the “aggregated powdered milk” described in this reference is a mixture of sugar and glucose and is said, “to be also suitable for use as an additive to coffee and black tea”. Thus, it does not use only powdered milk as an ingredient and cannot be employed as a substitute for breast milk for babies. In the Japanese Examined Patent Publication No. S49-4948, the “aggregated powdered milk” was obtained by using a mixture of powdered milk in a granulated state and sugar or glucose because of the problem of free fat arising when only the powdered milk is used as an ingredient. In the case of powdered milk in a granulated state, because the surface area increases by comparison with that in a solidified state, solubility is high despite the fact that the porosity of granules themselves is low.
Japanese Examined Patent Publication No. S45-39018 discloses technology similar to that disclosed in Japanese Examined Patent Publication No. 49-4948. Thus, it discloses that pore volume may be increased to obtain solid milk with good solubility and that a problem of free fat rises when the powdered milk is converted into solid milk. However, the same reference source describes that because “a limitation is placed on the increase in a single particle size of powdered milk” (ibid, second column, line 30), “readily soluble solid milk” is obtained by “causing the adhesion of powdered milk to sugars, granulating, and then molding and drying” (ibid, third column, lines 13 to 15). Thus, this reference also demonstrates that solid milk cannot be obtained by converting only the powdered milk into a solid state.
Japanese Patent Laid-open Publication No. S53-59066 discloses a “solid milk tablet”. In this high-density solid milk tablet, fat components leached out to the surface and milk is insulated from the external air with a fat film. The solid milk disclosed in this reference is preferably a high-density tablet and, therefore, the porosity thereof is low.
Japanese Patent No. 3,044,635 discloses, “frozen milk”. This frozen milk comprises a large amount of moisture for freezing and has practically no pores.
Solid food products that are dissolved when placed in hot water are known in the field of food products such as soups (Japanese Patent Laid-open Publication Nos. H11-127823, 2004-49220, and 2004-49221). Such products generally comprise a disintegrating agent. Furthermore, because ingredients are not powdered milk, the problem of free fat, which is inherent to powdered milk, is not encountered. Thus, solid soups are known, but if the technology of solid soup manufacture is simply diverted to the manufacture of solid milk, solid milk cannot be obtained because of a large amount of fat present in the powdered milk that is an ingredient for solid milk.
In the field of drugs, a variety of “tablets that rapidly disintegrate in oral cavity” have been disclosed (For example, Japanese Patent Laid-open Publication Nos. H5-271054, 8-291051, 2000-95674, 2000-44463, 2001-89398, and Japanese Patent No. 2,650,493). However, because the weight ratio of effective components in drug compositions is generally low, a large quantity of additives such as excipients can be compounded in addition to the effective components and the compositions are comparatively easy to design. Furthermore, they do not contain a large amount of fat as the powdered milk does. Therefore, the “rapid disintegration” technology employed in “tablets that rapidly disintegrate in oral cavity” cannot be directly diverted to solid milk. Furthermore, the “tablets that rapidly disintegrate in oral cavity” have to be rapidly dissolved with a very small amount of water present in the oral cavity. On the other hand, solid milk is generally drunk after dissolution in warm water and is not taken directly into the mouth. Therefore, rapid solubility of the order necessary for the “tablets that rapidly disintegrate in oral cavity” is not required.